cli: decode all cli arguments, assuming that they are utf-8 encoded

cli: decode all cli arguments, assuming that they are utf-8 encoded
Also encode all args to urllib as utf-8 because urllib doesn't handle unicode objects.
I'm not sure if it is appropriate to *assume* utf-8 encoding of cli args.  Perhaps the Right thing to do is to detect the platform encoding.  Any ideas?
This patch is mostly due to François Deppierraz.